Stephen Tobolowsky, in his new book The Dangerous Animals Club, has a great comment on drug use that really deconstructs our fascination with the practice – “[D]rugs create [an] … enticing arena where we can become addicted to the drama of our own bad choices” (pg. 129). He also performed the complete passage in the lit crawl as part of the Texas Book Festival.
Regarding motivations for drug use, there is escapism, and there is physical dependence. I would never discount these factors. But especially in youthful exuberance, there is an aspect of drug use that is like winding a top and letting spin just to see where it goes. It gives you an excuse to be a screw up. And to screw up. To test the boundaries of your own absurdity.